This invention relates to a magnetic disk device and, particularly, to a magnetic disk device for recording information into magnetic disks relying upon a vertical magnetic recording system.
In the magnetic disk devices in recent years, attempts have been made to improve the conventional longitudinal magnetic recording system and to develop a vertical magnetic recording system in an effort to increase the recording density.
A magnetic disk device which is based upon the vertical magnetic recording system, generally, uses a single magnetic pole head and a magnetic disk medium of a two-layer structure. In this magnetic disk device, the single magnetic pole head works to concentrate the external disturbing magnetic field entering from the exterior of the device, giving rise to a problem of destroying the data on the disk medium just under the recording magnetic pole of the single magnetic pole head. In the magnetic disk device employing the vertical magnetic recording system, therefore, a magnetic shielding function which prevents the entrance of the external magnetic field into the device plays a more important role than in the conventional device which utilizes the lengthwise magnetic recording system.
Therefore, there has heretofore been devised a magnetic disk device as indicated in JP-A-2003-77266 (patent document 1). The magnetic disk device of the patent document 1 comprises a rotary disk-type magnetic disk for recording information relying upon the vertical magnetic recording system, a magnetic head for recording information into the magnetic disk and for reproducing information from the magnetic disk, a disk drive mechanism for supporting the magnetic head in a manner to move in the radial direction of the magnetic disk, a housing having a base and a cover, and a magnetic shielding member constituted by using a magnetic member to magnetically shield the magnetic head.
In an embodiment illustrated in FIGS. 1 to 16 of the patent document 1, the housing accommodates therein the magnetic disk, magnetic head and disk drive mechanism, and a magnetic shielding member is provided over the upper surface, lower surface and side surfaces of the housing inclusive of the upper and lower sides over a range in which the magnetic head moves (prior art 1).
In an embodiment illustrated in FIG. 17 of the patent document 1, the housing accommodates therein the magnetic disk, the magnetic head, the disk drive mechanism and the magnetic shielding member, the magnetic shielding member being provided only over the base portion and the cover portion that are facing the magnetic head (prior art 2).
In an embodiment illustrated in FIG. 18 of the patent document 1, the housing accommodates therein the magnetic disk, the magnetic head and the disk drive mechanism, the housing is partly cut away, a magnetic shielding member is disposed therein, the front end side of the magnetic shielding member is extended to both sides of the magnetic disk, and the end surfaces thereof are faced to the end surface of the magnetic head (prior art 3).
In an embodiment illustrated in FIG. 19 of the patent document 1, the housing accommodates therein the magnetic disk, the magnetic head and the disk drive mechanism, a recessed portion is formed in the outer surface of the housing, a magnetic shielding member is disposed in the recessed portion, the front end side of the magnetic shielding member is extended to both sides of the magnetic disk, and the ends thereof are faced to the end of the magnetic head (prior art 4).